Teenagers unhappy with GCSE and A-level grades this summer may not be able to sit exams until November.

Ofqual, the exams regulator, said it hoped that A levels would be available to take in October and GCSEs a month later — six months after the exam season usually begins.

About a million students will be awarded grades that have been calculated by their teachers and moderated by the watchdog.

Ofqual said that every school should expect to have at least some of its grades changed. It warned that more weight would be given to the previous achievement of a school in a subject, than to a teacher’s opinion when finalising grades. This will prevent schools and colleges from giving top grades to too many pupils